A pressure sensor includes a sensor chip, a casing and an atmosphere introduction port. The sensor chip for detecting pressure is accommodated in the casing. The atmosphere pressure around the sensor is introduced into the casing through the atmosphere introduction port so that the sensor chip detects the objective pressure. The atmosphere introduction port is disposed on the casing. This type of pressure sensor is disclosed, for example, in Japanese Unexamined Patent Application Publications No. 2000-46673 and No. 2001-281086.
In general, in the sensor, the introduced atmosphere pressure is applied as a reference pressure to one side of the sensor chip. The objective pressure as a measuring object is applied to the other side of the sensor chip. Therefore, the sensor chip detects a difference between the reference pressure and the objective pressure so that the sensor detects the object pressure relatively. Thus, the sensor provides a relative pressure sensor.
The atmosphere introduction port includes a filter disposed on an outer opening of the port. The filter is made of, for example, goatex and the like. The goatex is produced by Japan Goatex Co., LTD under the trade name of GOATEX. The filter passes only gas without passing moisture, so that the filter prevents water drop such as rainwater from penetrating into the casing through the atmosphere introduction port. However, it is necessary to use special techniques such as a supersonic adhesion method and special material such as goatex with a special adhesive film. Therefore, a manufacturing cost of the sensor is increased.